Extruder feed system

ABSTRACT

Extruder feed system. The system includes a pair of spaced-apart, internally and oppositely threaded rotatable elements for receiving and engaging a plastic filament material. An electric motor rotates the rotatable elements in opposite directions thereby to drive the filament into a liquefier chamber for subsequent discharge through a nozzle. The system provides very accurate layer-by-layer build up.

This application claim priority to provisional application Ser. No.61/863,110 filed on Aug. 7, 2013, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

This invention relates to an extruder, and more particularly, to anextruder used in an additive manufacturing device employing a screwdrive.

Additive manufacturing devices such as 3-D printers build up an objectlayer-by-layer by extruding a filament material onto a support surface.The quality of the object produced depends in large measure on tightcontrol of the flow rate of filament material through the extruder inconjunction with control of the X-Y position of the extruder head as ittraverses an area to build up a layer.

A prior art extruder system is shown schematically in FIG. 1. Filamentmaterial 10 passes through a pinch roller feed system 12 that drives thefilament material 10 downwardly into a liquefier chamber 14. Thereafter,filament material is discharged through a nozzle 16 onto a scaffolding18. The pinch roller system 12 engages the filament material 10 on eachside as it drives the filament material into the liquefier chamber 14.The driving forces that can be achieved with the arrangement in FIG. 1is limited. Further, the arrangement shown in FIG. 1 is not as accurateas desired because of step size limitations in motor systems driving thepinch rollers.

It is also known to use an internally threaded nut to drive a filamentinto a liquefier chamber. In this case, the filament passes through aninternally threaded nut which, upon rotation, drives the filamentmaterial linearly. However, the nut rotation puts an unwanted torque onthe filament causing it to distort as it is driven linearly.

An object of the present invention is a screw drive employingcounter-rotating elements to substantially eliminate the unwanted torquewhile driving the filament into the extruder.

SUMMARY OF THE INVENTION

The extruder feed system according to the invention includes a pair ofspaced-apart, internally and oppositely threaded rotatable elements forreceiving and engaging a filament material. A motor is provided forrotating the rotatable elements in opposite directions, thereby to drivethe filament into a liquefier chamber for subsequent discharge through anozzle. In a preferred embodiment, the system includes a gear traindriven by the motor to rotate the rotatable elements in oppositedirections. A suitable motor is a stepper motor or a DC motor. Thefilament material may be plastic.

In a preferred embodiment, they gear train includes beveled gears drivenby the motor. The gear train may include a belt or cable driven withpulleys.

In yet another embodiment, the system of the invention further includesa control loop for controlling power of the motor, thereby to controlthe filament material extrusion rate.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of a prior art additive manufacturingextruder system.

FIG. 2 is a schematic illustration of a pair of counter-rotatable hexnuts for driving a filament material.

FIG. 3 is a cross-sectional view of an embodiment of the inventiondisclosed herein utilizing a motor, a flow controller and bevel gearsdriving the counter-rotating bevel gears.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 2, filament material 10 is seen passing throughthe interior of first and second hex nuts 20 and 22. The hex nut 20 isinternally threaded in, for example, a right-handed thread pattern.Similarly, the hex nut 22 is infernally threaded to have the oppositedirection for the threads, such as a left-handed thread pattern. It ispreferred that the diameter of the filament 10 be slightly oversizedwith respect to the tapped hole through the hex nuts 20 and 22. As canbe seen in the figure, the hex not 20 is rotated in a counterclockwisedirection and the hex nut 22 is rotated in a clockwise direction.Because the threads of the counter rotating hex nuts 20 and 22 areoppositely directed, the filament material 10 is driven downwardly inFIG. 2.

Importantly, because the hex nuts 20 and 22 are counter-rotating,material distortion resulting from torque between the two hex nuts issubstantially eliminated as the counter-rotating nuts balance out thetorque effects.

An embodiment of the present invention is shown in FIG. 3. A frame 30supports for rotation bevel gears 32, 34 and 36. A motor 38 under thecontrol of a flow controller 40 rotates the bevel gear 32. The bevelgear 32 operatively engages the bevel gears 34 and 36 driving thesebevel gears in opposite rotational directions. As will be appreciated,the interior of the bevel gear 34 is threaded in a first sense, such asright-handed, and the bevel gear 36 is internally threaded in theopposite sense such as left-handed. When the motor 38 is activated undercontrol of the flow controller 40, the filament 10 will be driven into aliquefier chamber as shown in FIG. 1. The motor 38 may be a steppermotor or a DC motor. The motor may be a pneumatic motor, internalcombustion engine or an AC motor. The arrangement of the motor 38 shownin FIG. 3 assures that the flow rate of filament 10 material through thesystem can be precisely controlled.

Those of skill in the art will recognize that separate motors could beused to drive the rotatable elements if desired. It is also noted thatthe space between the bevel gears 34 and 36 should be made small tominimize distortion of the filament passing through the counter-rotatingbevel gears. The gap in FIG. 3 is exaggerated for clarity.

The inventors herein have determined that driving the bevel gears 34 and36 at the same speed in opposite directions isn't sufficient to ensure aconstant extrusion rate due to variabilities in the diameter of thefilament 10 and other physical inconsistencies. The inventors haveanalytically determined that there is a direct relationship between theextrusions rate and the input electrical power to the motor 38 using thescrew drive of the invention. In particular, the inventors havedetermined that the extrusion rate Q=kIV. That is to say, filament flowrate Q is linearly proportional to power (IV) on the motor 38. As anexample, if one wishes to have a constant flow rate, the electricalpower to the motor 38 is held constant (that is to say, the product ofmotor current (I) and motor voltage (V) is held constant). To increaseor decrease the flow rate, the motor 38 voltage is controlled via a PWMcontrol on the motor 38. Thus, filament flow rate is controlled bycontrolling power to the motor 38. The flow controller 40 may include aconventional control loop employing PID control for example.

It is recognized that modifications and variations of the presentinvention will be apparent to those of ordinary skill in the art and itis intended that all such modifications and variations be includedwithin the scope of the appended claims.

What is claimed is:
 1. Extruder feed system comprising: a pair ofspaced-apart, internally and oppositely threaded rotatable elements forreceiving and engaging a filament material; an electrical motor forrotating the rotatable elements in opposite directions thereby to drivethe filament into a liquefier chamber for subsequent discharge through anozzle; and further including a control loop for controlling the productof motor current and motor voltage thereby to control the filamentmaterial extrusion rate that is linearly proportional to the product ofmotor current and motor voltage.
 2. The system of claim 1 furtherincluding a gear train driven by the motor to rotate the rotatableelements in opposite directions.
 3. The system of claim 1 wherein themotor is a stepper motor.
 4. The system of claim 1 wherein the motor isa DC motor.
 5. The system of claim 2 wherein the gear train includes abeveled gear driven by the motor.
 6. The system of claim 1 wherein therotatable elements are internally threaded hex nuts.
 7. The system ofclaim 1 wherein the motor is an AC motor.
 8. The system of claim 2wherein the gear train includes a belt or cable driven with pulleys.